Field of the Invention
The present invention relates to an optical fiber connection structure and an optical fiber connector which optically connect optical fibers to each other.
Description of Related Art
A so-called field assembly optical connector as an optical connector which allows assembly work to be easily performed with respect to a tip of an optical fiber on site is well known. In the related art, as a field assembly optical connector, a field assembly optical connector is known which includes a short optical fiber (bare optical fiber, and hereinafter, also referred to as a built-in optical fiber) which is inwardly inserted into and fixed to a ferrule, and a mechanical splice type clamp portion which is provided on a rear side opposite to a front end surface of the ferrule for butting (for example, refer to FIGS. 2 to 5 of Japanese Unexamined Patent Application, First Publication No. 2011-33731).
The clamp portion of the field assembly optical connector includes a base member, a cover member, and a plate spring which elastically biases the cover member toward the base member. A rear end portion of the built-in optical fiber is disposed between the base member and the cover member of the clamp portion. Another optical fiber (for example, an optical fiber core wire, and hereinafter, also referred to as an insertion optical fiber), which is inserted between the base member and the cover member of the clamp portion from a rear side opposite to the ferrule side, can be butt-connected to a rear end of the built-in optical fiber. In the field assembly optical connector, the rear end portion of the built-in optical fiber, and a tip portion of the insertion optical fiber which is butt-connected to the rear end of the built-in optical fiber are held between the base member and the cover member of the clamp portion so as to be fixed by elasticity of the plate spring, and the rear end portion of the built-in optical fiber is assembled to the tip of the insertion optical fiber.
In the field assembly optical connector, in order to decrease connection loss, a liquid refractive index matching agent such as silicone-based grease is provided on a butt-connection portion between the built-in optical fiber and the insertion optical fiber (for example, refer to FIG. 16(c) of Japanese Unexamined Patent Application, First Publication No. 2011-33731)
In addition, in the field assembly optical connection, it is suggested that a light-transmitting solid refractive index matching material formed of a polymer material be provided on the rear end of the built-in optical fiber, and the insertion optical fiber and the built-in optical fiber having tips abutting on the solid refractive index matching material be optically connected to each other via the solid refractive index matching material (for example, refer to FIGS. 7(a) and 7(b) or the like of Japanese Unexamined Patent Application, First Publication No. 2011-33731).
In general, a rear end surface (an end surface of a rear end side opposite to the tip exposed to a joining end surface of the ferrule) of the built-in optical fiber of the field assembly optical connector is configured of a flat surface perpendicular to an optical axis of the built-in optical fiber. Meanwhile, a coating material of the tip of the insertion optical fiber is removed on site, the bare optical fiber is led out, the tip of the bare optical fiber is cut, thereafter, the tip of the bare optical fiber is inserted into the clamp portion from the rear side of the clamp portion, and the tip of the bare optical fiber is butted to the rear end of the built-in optical fiber. Cutting of the bare optical fiber (hereinafter, also referred to as an insertion-side bare optical fiber) is performed using a dedicated cleaver (cutter), and a flat mirror-shaped tip surface perpendicular to the optical axis of the bare optical fiber is formed on the bare optical fiber. However, cutting of the insertion side bare optical fiber may not be correctly performed on site, and irregularities may be formed on the tip of the insertion side bare optical fiber.
In the configuration in which the liquid refractive index matching agent is provided in the butt-connection portion between the built-in optical fiber and the insertion optical fiber, a portion between the tip of the insertion side bare optical fiber on which irregularities are formed and the rear end surface of the built-in optical fiber abutting on the tip of the insertion side bare optical fiber can be embedded with the liquid refractive index matching agent. As a result, it is possible to decrease connection loss.
However, in this case, concave portions of the irregularities on the tip of the insertion side bare optical fiber abut on an edge portion on an outer circumference of the rear end surface of the built-in optical fiber, cracks occur on the edge portion, and deterioration of mechanical characteristics of the rear end of the built-in optical fiber may occur. In addition, fragments generated by the cracks are interposed between the built-in optical fiber and the insertion side bare side optical fiber, and the fragments may obstruct the butt-connection.
In the configuration in which the solid refractive index matching material is provided on the rear end of the built-in optical fiber of the field assembly optical connector, it is possible to allow the solid refractive index matching material to function as a cushion layer. Accordingly, in this configuration, since the portion between the tip of the insertion side bare optical fiber on which irregularities are formed and the rear end surface of the built-in optical fiber can be embedded with the solid refractive index matching material, it is possible to realize an optical connection having low loss. In addition, since the solid refractive index matching material functioning as the cushion layer abuts on the convex portion of the tip of the insertion side bare optical fiber, cracks in the edge portion on the outer circumference of the rear end surface of the built-in optical fiber are effectively prevented from occurring.
However, in the configuration in which the solid refractive index matching material is provided on the rear end of the built-in optical fiber of the field assembly optical connector, when air is interposed between a core portion (or a mode field diameter portion) of the tip of the insertion side bare optical fiber particularly, and the solid refractive index matching material, connection loss is greatly influenced, and an optical connection cannot be performed. Accordingly, in this configuration, it is necessary to press the tip of the insertion side bare optical fiber to the refractive index matching material so as to securely come into close contact with each other. However, when close contact of the tip of the insertion side bare optical fiber with respect to the solid refractive index matching material is held and the field assembly optical connection is assembled to the tip of the insertion optical fiber, the tip of the insertion side bare optical fiber may be separated from the solid refractive index matching material due to unexpected tension of the insertion optical fiber 1 or the like, and operation may need to be performed again.
The present invention is made in consideration of the above-described problems, and is to provide an optical fiber connection structure and an optical fiber connector capable of preventing the occurrence of cracks in optical fibers due to abutment of optical fibers in a clamp portion, and of easily improving efficiency of an operation of optically connecting the optical fibers to each other in the clamp portion and holding and fixing the optical fibers.